He added: "When the bug is circulating widely, people become exposed without realising and develop immunity. For a few years, levels of the illness drop, until the next generation are vulnerable to the bacteria."

Symptoms include a sore throat and a rash across the neck and chest. This spreads over limbs within a day.

Sufferers' cheeks can be flushed and their tongues can develop a thick white coating.

It is usually treated with antibiotics. But if left untreated, it can lead to blood poisoning and toxic shock syndrome.